Elongated Heterometal Double-Sites Promote Nitrogen Reduction on Two-Dimensional MM’B7 Monolayers

2021 
The efficient activation of the adsorbed N2 is the initial and crucial step in the electrochemical nitrogen reduction reaction (NRR), but remains a long-standing challenge. Attaching long-distance heterometal M and M′ metals from the two ends of NN (like a curved bonding in Ag2C2) is an ingenious strategy to promote the activation and polarization of the intrinsic triple bond during electrocatalysis. Motivated by this strategy and the excellent stability and larger size of the B7-unit, the global-minimum MM′B7 monolayers with elongated heterometal double-sites as promising NRR electrocatalysts have been identified from the 10 179 candidates using high-throughput screening. The TiNbB7 monolayer with a metal distance of 3.56 A exhibits the optimal NRR catalytic activity with the limiting potential of 0.04 V and the kinetic energy barrier of 0.75 eV through the mixed mechanism, together with a strong capability of suppressing the competitive hydrogen evolution reaction and the surface oxidation. The other eight global-minimum systems (NbMoB7, ScHfB7, ScNbB7, ScTaB7, ScZrB7, TiHfB7, TiNbB7 and ZrHfB7) also possess excellent catalytic activity, and the highest limiting potential is only 0.62 V. These data adequately verify that long-distance heterometal double-sites are an excellent strategy to active and polarize the NN triple bond due to the elongated bonding length, asymmetric interaction and favorite orbital matching for the side-on adsorbed N2 molecule on double-sites. Most importantly, this work opens a new avenue to design and develop efficient NRR electrocatalysts with the long-distance heterometal double-sites.
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